Hearing aid apparatus



March 31, 1964 P. J. MCGEE HEARING AID APPARATUS Filed Jan. 31, 1962 2Sheets-Sheet 1 INVENTOR. Paui r1 m Gee (iliiy March 31, 1964 P. J. MCGEE3,126,977

HEARING AID APPARATUS Filed Jan. 51, 1962 2 Sheets-Sheet 2 INVENTOpauinf. 777 e'e BY 2 f a/Z i Zy.

United States Patent 3,126,977 HEG All) APPARATUS Paul J. McGee,Chicago, Ill., assignor to Zenith Radio Corporation, a corporation ofDelaware Filed Jan. 31, 1962, Ser. No. 170,211 4 Claims. (Cl. 181-23)This invention relates in general to the hearing aid art and moreparticularly to frequency-selective filtering apparatus for effectivelyfiltering the sound delivered from the output transducer of a hearingaid in order to remove certain frequency components before the soundenergy reaches the wearers auditory canal.

Many hard-of-hearing individuals experience a sensoryneural hearing lossor impairment; namely, normal hearing of the low audible frequencies(for example, below 1,000 cycles per second) is enjoyed, whereas thereis a severe loss as to the components in the remainder of the audiblefrequency spectrum. When those individuals attempt to improve theirhearing by means of a conventional hearing aid, it is found that theamplified low frequency components reaching the ear drum are so loudthat they mask out the high frequencies. Overamplification of the lowfrequency components creates an unpleasant sensation varying fromdiscomfort to pain. As a consequence of such discomfort, a person with asensory-neural high frequency impairment usually does not use a hearingaid.

Of course, the frequency response characteristic of the input transduceror microphone, the signal amplifying apparatus, and/or the soundreproducer of a conventional hearing aid may be altered to delete thelow frequencies of the acoustic energy. However, this has not proved tobe an acceptable solution to the problem.

The present invention solves the problem and provides filteringapparatus for removing the low frequency components from the soundproduced by the hearing aid out put transducer while at the same timepermitting those same low frequencies to by-pass the hearing aidentirely and reach the auditory canal in normal fashion.

Accordingly, it is an object of the present invention to provide new andimproved apparatus for use in conjunction with a hearing aid or thelike.

It is another object of the invention to provide a useful hearing aidarrangement for an individual with a sensory-neural high frequencyhearing loss.

It is a further object of the invention to, provide a relatively simpleand inexpensive filter for removing certain frequency components fromthe acoustic energy developed in a hearing aid output transducer.

The invention provides, in accordance with one of its aspects, apparatusfor use in conjunction with a hearing aid having an input transducerresponsive to received acoustic energy having frequency componentsextending over a given frequency range, and an output transducer,mounted in close proximity to the input transducer, for developingamplified acoustic energy having frequency components extending oversubstantially the same given range. The apparatus comprises an ear moldfor acoustically sealed insertion in a human ear and having a soundpassageway therethrough communicating with the auditory canal, plus anacoustic connecting device, coupled to the output transducer, to beattached to the ear mold for extending the sound passageway to theoutput transducer to channel the amplified acoustic energy to theauditory canal. At least one aperture is provided venting the soundpassageway directly to the outside atmosphere efiectively to attenuatethe relatively low frequency components of the amplified acousticenergy, thereby to permit primarily the relatively high frequencycomponents to reach the auditory canal. Finally, the

3,126,977. Patented Mar. 31, 1964 apparatus includes a low-pass filterelement disposed in the aperture for permitting the translation throughthe aperture of the low frequency components while preventing thetranslation of the high frequency components through the aperture inorder to preclude acoustic feedback of the high frequency componentsfrom the output to the input transducer.

The features of this invention which are believed to be new are setforth with particularity in the appended claims. The invention, togetherwith further objects and advantages thereof, may best be understood,however, by reference to the following description in conjunction withthe accompanying drawings, in which FIGURES 1-5 collectively illustratea hearing aid apparatus constructed in accordance with one embodiment ofthe invention.

Consideration will now be given to FIGURES 1-5 wherein the invention isillustrated in connection with a conventional eye glass hearing aid ofthe type in which the input and output transducers and the amplifyingcircuitry are all contained within a side member or temple bar 2 of aspectacle frame. The input transducer or microphone is designated bynumeral 3, the output transducer or sound-reproducing device by numeral4, the amplifying circuitry by indicia 5, the battery power supply by 6,and the conventional off-on switch and volume control by 7. Of course,the details of these components and the connecting circuitry are wellknown in the art and have not been shown in order to simplify thedrawmgs.

An ear mold 10 preferably is customized to fit tightly in the ear of theparticular wearer. In any event, ear mold 1% preferably should form asubstantially complete acoustic seal upon insertion in the wearers ear.Although it is not necessary, in the illustrated embodiment a portion ofthe canal insert of the ear mold has been cut away and the ear mold hasbeen hollowed out to form an acoustic cavity or chamber 12. Cavity 12'is provided with an opening surrounded by a metallic ring washer 13embedded in the ear mold in order that a sound passageway may extendthrough the ear mold from the external portion thereof in the directionto communicate with the auditory canal of the persons ear when car mold10 is properly inserted.

As illustrated, output transducer 4 is not located immediately adjacentear mold 10 but is positioned a relatively short distance away.Specifically, it is contemplated that the invention will be employed inconnection with ear-level hearing aids in which the input and outputtransducers and the customary signal amplifying circuitry are positionedin close proximity to the wearers ear, for example being mounted withina spectacle frame as shown in the illustrated embodiment, or within ahousing shaped and dimensioned to be positioned behind the wearers ear.In any case, the output transducer would be only a couple inches awayfrom ear mold 10.

An acoustic connecting device 15 is attached to ring 13 of ear mold inconventional fashion and is coupled by means of an air conduction tube16 to output transducer 4 to extend the sound passageway 12 of the earmold to the output transducer in order to channel the amplified acousticenergy from the transducer to the auditory canal. Connecting device 15may be constructed of plastic, metal or any suitable material. It has aprotruding portion 15a which is dimensioned with respect to the insidediameter of ring 13 such that the connecting device may be insertedwithin the ring with a fairly snug fit. A split spring 13a is providedin metal retainer ring 13 in order to provide .a conventional snap ringtype of connection between connecting device 15 and ear mold 10.

Apair of apertures 18 are provided in ear mold 10 for venting soundpassageway 12 directly to the outside atmosphere. While two such holes18 are shown in the illustrated embodiment, in certain cases only oneneed be employed whereas in others three or more may be found helpful.The length and diameter of each aperture 18, the number of suchapertures, and the volume of cavity 12 determine the frequency responseof the filtering apparatus of the invention. A low pass filter element21, in the form of common felt, is disposed or inserted in each aperture18 where those apertures open to the outside atmosphere.

In operation, the input and output transducers and the amplifyingcircuitry in the ear-level hearing aid function in conventional manner.Briefly, input transducer 3 responds to received acoustic energy havingfrequency components extending over a given frequency range to developan electrical signal, amplifier 5 amplifies that signal and translatesit to output transducer 4 which .in turn responds thereto and developsamplified acoustic energy having frequency components extending oversubstantially the same given range. In the absence of apertures 18 inear mold 10, substantially all of the frequency components of theamplified acoustic energy would be channeled via air conduction tube 16,connecting device 15, and sound passageway 12 to the auditory canal.

With the presence of apertures 18, however, and in accordance with theinvention, the output transducer 4 is effectively loaded as to the lowfrequencies such that those frequencies are attenuated considerably. Toelucidate, each of apertures 18 has a certain inertance which is aproperty of the length and diameter of the hole. Inertance, of course,is the acoustical equivalent of inductance. This inertance appears inshunt with the output of the output transducer. Since the effect ofinertance varies with frequency, presenting a lower impedance to the lowfrequencies with respect to the impedance presented to the highfrequencies, holes 18 effectively shunt out to the atmosphere the lowfrequency components. By proper design, holes 18 may be arranged to havea negligible effect on the high frequencies since the shunting inertanceprovides a high impedance, and thus all of the amplified high frequencycomponents are delivered to the auditory canal and ultimately to thepersons ear drum. In this Way, the maximum gain of which the system iscapable is utilized to amplify the high frequencies and to provide theindividual with a sensoryneural loss the frequency components which henormally cannot hear. On the other hand, the low frequency components,which he can hear normally, are in a sense dumped through apertures 18directly to the outside atmosphere so that they do not reach the personsear drum and drown out the high frequencies.

Preferably, the ear mold should be customized for the particular wearerin order that an optimum frequency response is realized. Lengtheningapertures 18 and/or reducing their diameter increases the inertance andtherefore decreases the number of low frequency components (i.e.,narrows the band) shunted to the atmosphere. Increasing the number ofapertures 18 lowers the effective inertance and therefore widens theband of low frequencies prevented from reaching the persons ear drum. Inaddition, increasing the volume of cavity 12 decreases the number of lowfrequency components shunted to the atmosphere. It has been found thatoptimum results can best be achieved for any given individual With asensory-neural loss by empirical methods.

While holes 18 preferably should present a high impedance to the highfrequency components so that the net effect is that the holes are noteven present with respect to the high frequencies, there may be a smallamount of high frequency acoustic energy that will tend to leak outthrough apertures 18. If the microphone is not mounted in closeproximity to the output transducer, these high frequency components willnot have any deleterious effect on'the operation of the system. However,when the transducers are located relatively close to each other, as isthe case when an ear-level aid is employed, the high frequencies thatleak out through apertures 18 may possibly cause objectionable acousticfeedback from the output to the input transducer, thereby initiatingannoying acoustic feedback oscillations. In accordance with a feature ofthe invention, such acoustic feedback is precluded by low pass filter 21in each hole 18 which effectively blocks the high frequencies fromreaching the outside atmosphere. Element 21 is frequency selective inthat it permits low frequencies to pass therethrough with negligibleresistance while at the same time it presentsan extremely highresistance to the translation of high frequency sound energy.

The low frequency components translated from cavity 12 to the outsideatmosphere via filter elements 21 do not initiate acoustic feedbackoscillations. This obtains since the filtering action of apertures 18causes the system to have insufficient gain at those low frequencies toeffect acoustic feedback oscillations.

Since different types of common felt exhibit different frequencyresponse characteristics, the response of filter elements 21 may beoptimized by proper selection of the felt material. Once again, it hasbeen found that best results can be obtained by empirical methods.

Of course, it is desirable that low pass filter elements 21 permit thetranslation therethrough of the amplified low frequencies in order thatthey may be prevented from reaching the auditory canal. At the sametime, elements 21 pass the low frequencies directly from the outsideatmosphere through apertures 18 to the auditory canal in normal fashion.Since the person with a sensory-neural high frequency hearing impairmentcan hear the low frequencies normally, it is extremely advantageous topermit those frequencies to reach the persons ear drum in normal manner,and this is possible by means of apertures 18 and filter elements 21.Thus, the low frequencies produced in the output transducer areeffectively prevented, by means of apertures 18, from reaching thepersons auditory canal, while at the same time the same apertures 18permit the low frequencies to by-pass the hearing aid system and reachthe auditory canal in customary manner.

The invention is obviously not limited to the arrangement in which theconnecting device is coupled to the output transducer by way of an airtube but may be applied to the case where the connecting device, to beattached to the ear mold, is rigidly coupled to the output transducer,namely when the output transducer is positioned right at or immediatelyadjacent the ear mold. In that arrangement, the amplifying circuitry maystill be mounted within a spectacle frame or in a casing positionedbehind the ear and an electrical connection is provided to the outputtransducer.

Of course, it is not necessary that apertures 18 be provided in the earmold itself; all that is necessary is that at least one aperture bepositioned at some point along the sound passageway between the outputtransducer and the auditory canal in order that the passageway is venteddirectly to the outside atmosphere.

A novel frequency-selective filtering apparatus is thus provided whichattenuates the low frequency components developed in the outputtransducer of a hearing aid, permits those same low frequencies toby-pass the hearing aid and reach the auditory canal, while at the sametime prevents acoustic feedback of the high frequencies from the outputtransducer to the input transducer.

While a particular embodiment of the invention has been shown anddescribed, modifications may be made, and it is intended in the appendedclaims to cover all such modifications as may fall within the truespirit and scope of the invention.

I claim:

1. Apparatus for'use in conjunction with a hearing aid having an inputtransducer responsive to received acoustic energy having frequencycomponents extending over a given frequency range, and an outputtransducer, mounted in close proximity to said input transducer, fordeveloping amplified acoustic energy having frequency componentsextending over substantially said same given range, comprising:

an ear mold for acoustically sealed insertion in a human ear and havinga sound passageway therethrough communicating with the auditory canal;

an acoustic connecting device coupled to said output transducer and tosaid ear mold for extending said sound passageway to said outputtransducer;

said ear mold having at least one aperture venting said sound passagewaydirectly to the outside atmosphere effectively to attenuate therelatively low frequency components of said amplified acoustic energywithin said frequency range, thereby to permit primarily the relativelyhigh frequency components within said range to reach the auditory canal;

and a low-pass filter element insert disposed in said aperture forpermitting the translation through said aperture of said low frequencycomponents while preventing the translation of said high frequencycomponents through said aperture in order to preclude acoustic feedbackof said high frequency components from said output to said inputtransducer.

2. Apparatus for use in conjunction With a hearing aid having an inputtransducer responsive to received acoustic energy having frequencycomponents extending over a given frequency range, and an outputtransducer, mounted in close proximity to said input transducer, fordeveloping amplified acoustic energy having frequency componentsextending over substantially the same given range, comprising:

an ear mold to be coupled to said output transducer and to be insertedin a human ear and having a sound passageway for coupling said outputtransducer to the auditory canal to channel said amplified acousticenergy to the auditory canal;

said ear mold having at least one aperture venting said sound passagewaydirectly to the outside atmosphere effectively to attenuate therelatively low frequency components of said amplified acoustic energywithin said frequency range, thereby to permit primarily the relativelyhigh frequency components within said range to reach the auditory canal;

and a low-pass filter element insert disposed in said aperture forpermitting the translation through said aperture of said low frequencycomponents while preventing the translation of said high frequencycomponents through said aperture in order to preclude acoustic feedbackof said high frequency components from said output to said inputtransducer.

3. Apparatus for use in conjunction with a hearing aid having an inputtransducer responsive to received acoustic energy having frequencycomponents extending over a given frequency range, and an outputtransducer, mounted in close proximity to said input transducer, fordeveloping amplified acoustic energy having frequency componentsextending over substantially said same given range, comprising:

an ear mold for acoustically sealed insertion in a human 2'5 ear andhaving a sound cavity communicating With the auditory canal; an acousticconnecting device, coupled to said output transducer, to be attached tosaid ear mold for com municating said sound cavity with said outputtrans ducer to channel said amplified acoustic energy to the auditorycanal; said ear mold having at least one aperture venting said soundcavity directly to the outside atmosphere effectively to attenuate therelatively low frequency components of said amplified acoustic energywithin said frequency range, thereby to permit primarily the relativelyhigh frequency components within said range to reach the auditory canal;and a low-pass filter element insert disposed in said aperture forpermitting the translation through said aperture of said low frequencycomponents while preventing the translation of said high frequencycomponents through said aperture in order to preclude acoustic feedbackof said high frequency components from said output to said inputtransducer. 4. Apparatus for use in conjunction with a hearing aidhaving an input transducer responsive to received acoustic energy havingfrequency components extending over a given frequency range, and anoutput transducer, mounted in close proximity to said input transducer,for developing amplified acoustic energy having frequency componentsextending over substantially said same given range, comprising:

an ear mold device for acoustically sealed insertion in a human ear andhaving a sound passageway therethrough communicating with the auditorycanal;

an acoustic connecting device, coupled to said output transducer, to beattached to said ear mold for extend-- ing said sound passageway to saidoutput transducer to channel said amplified acoustic energy to theauditory canal;

one of said devices having at least one aperture for venting said soundpassageway directly to the outside atmosphere effectively to attenuatethe relatively low frequency components of said amplified acousticenergy within said frequency range, thereby to permit primarily therelatively high frequency components within said range to reach theauditory canal;

and a low-pass filter element insert disposed in said aperture forpermitting the translation through said aperture of said low frequencycomponents while preventing the translation of said high frequencycomponents through said aperture in order to preclude acoustic feedbackof said high frequency components from said output to said inputtransducer.

References Cited in the file of this patent UNITED STATES PATENTS1,964,604 Swickard June 26, 1934 2,312,534 Fiene Mar. 2, 1943 2,363,175Grossman Nov. 21, 1944 2,437,490 Watson et al. Mar. 9, 1948 2,506,490Coley May 2, 1950 2,874,231 Wallace Feb. 17, 1959 2,933,145 Di MattiaApr. 19, 1960 3,068,954 Strzalkowski Dec. 18, 1962

1. APPARATUS FOR USE IN CONJUNCTION WITH A HEARING AID HAVING AN INPUTTRANSDUCER RESPONSIVE TO RECEIVED ACOUSTIC ENERGY HAVING FREQUENCYCOMPONENTS EXTENDING OVER A GIVEN FREQUENCY RANGE, AND AN OUTPUTTRANSDUCER, MOUNTED IN CLOSE PROXIMITY TO SAID INPUT TRANSDUCER, FORDEVELOPING AMPLIFIED ACOUSTIC ENERGY HAVING FREQUENCY COMPONENTSEXTENDING OVER SUBSTANTIALLY SAID SAME GIVEN RANGE, COMPRISING: AN EARMOLD FOR ACOUSTICALLY SEALED INSERTION IN A HUMAN EAR AND HAVING A SOUNDPASSAGEWAY THERETHROUGH COMMUNICATING WITH THE AUDITORY CANAL; ANACOUSTIC CONNECTING DEVICE COUPLED TO SAID OUTPUT TRANSDUCER AND TO SAIDEAR MOLD FOR EXTENDING SAID SOUND PASSAGEWAY TO SAID OUTPUT TRANSDUCER;SAID EAR MOLD HAVING AT LEAST ONE APERTURE VENTING SAID SOUND PASSAGEWAYDIRECTLY TO THE OUTSIDE ATMOSPHERE EFFECTIVELY TO ATTENUATE THERELATIVELY LOW FREQUENCY COMPONENTS OF SAID AMPLIFIED ACOUSTIC ENERGYWITHIN SAID FREQUENCY RANGE, THEREBY TO PERMIT PRIMARILY THE RELATIVELYHIGH FREQUENCY COMPONENTS WITHIN SAID RANGE TO REACH THE AUDITORY CANAL;AND A LOW-PASS FILTER ELEMENT INSERT DISPOSED IN SAID APERTURE FORPERMITTING THE TRANSLATION THROUGH SAID APERTURE OF SAID LOW FREQUENCYCOMPONENTS WHILE PREVENTING THE TRANSLATION OF SAID HIGH FREQUENCYCOMPONENTS THROUGH SAID APERTURE IN ORDER TO PRECLUDE ACOUSTIC FEEDBACKOF SAID HIGH FREQUENCY COMPONENTS FROM SAID OUTPUT TO SAID INPUTTRANSDUCER.